Electric motors arm used in a variety of electrical equipment. In particular, they are used in various manufacturing equipment. For example, linear electric motors produce electrical power that propels an annature in one dimension. Wafer stages positioning silicon wafers during photolithography and other semiconductor processing equipment utilize linear electric motors to position the wafer.
A typical linear electric motor has a magnet track with pairs of opposing magnets facing each other. Within spaces between the pairs of opposing magnets, an armature moves. The armature has windings of a conductor which are connected to an electrical current. When the electrical current is turned on, electromagnetic fields arc created within the windings. Those electromagnetic fields interact with the magnetic fields of the magnet pairs to cause the armature to move. When the armature is attached to a wafer stage, the wafer stage moves in concert with the armature, FIGS. 1a and 1b Illustrate a conventional magnet track 100 used in an electric motor. FIG. 1a is a perspective view of the magnet track 100, and FIG. 1b is a cross-sectional front view of the magnet track 100. The magnet track 100 has pairs of opposing magnets 102 along the length of the magnet track 100. An armature is inserted into the magnet track and is powered by electrical current to cause the armature to move with respect to the magnet track 100.
In a multiphase motor, the armature has various windings grouped into phases. The phase groups are selectively pulsed with electric current to create a more efficient motor. As the armature moves within the magnet track 100 as a first group of coils is pulsed, the first group moves out of its optimal position between the pairs of magnets 102. Then, it becomes more efficient to pulse a second group of windings. More phase groups are theoretically more efficient since a more even application of force and utilization of power input is maintained. However, each additional phase group complicates a timing of the pulses to the various phase groups. Presently, three-phase motors and armatures have gained favor in balancing these considerations.
Two examples of conventional multi-phase electric motors are given in the patents to Beakley et al. (U.S. Re. 34,674) and Phillips (U.S. Pat. No. 4,767,954) both of which are incorporated by reference herein in their entirety. Both patents illustrate conventional manufacturing difficulties. Beakley et al. has multiple sizes of individual windings which make up the armature. For example, FIG. 5 in Beakley et al., shows an arrangement of windings requiring an intricate placement of the different size windings with respect to each other. A requirement for multiple sizes of windings complicates manufacture of the armature, and hence the motor, since each size winding would typically have a separate manufacturing process for its construction. In addition, it may be more difficult to align windings of different shapes or sizes.
Although Phillips teaches an armature where all the windings have the same regular shape, the Phillips windings must be carefully aligned. FIG. 2 in Philips shows the alignment of windings to make up the Phillips armature. Similarly, FIG. 2 in the present application shows a top cross-sectional view of the magnet track 100 and an annature 200 in accordance with Phillips. In FIG. 2, corresponding phases have the same letter, and cross-sections which are part of the same winding have the same number. For example, cross-sections labeled A0, A1, A2, and A3 are part of the same phase group. Similarly, cross-sections B0, B1, B2, and B3 are part of another phase group, and cross-sections C0, C1, C2, and C3 are part of a third phase group. A winding such as A1 has a low side 202 aligned with a high side 204 of an adjacent winding A2 in the same phase group. Similarly, a low side 206 of A2 is aligned with a high side 208 of A3 in the same phase group. All the windings in all the phase groups A, B, C are aligned in this fashion. Misalignment of windings will cause inefficiencies in the motor's operation.
By having the conductor density in the armature residing between the pairs of opposing magnets as high as possible, high efficiency of the electric motor, measured as force output compared with a square root of power dissipation in the windings, is obtained.
What is needed is an armature with regular windings of all the same shape that also maximize a wire density within the magnet gap. Such regular windings would improve manufacturability while providing high efficiency of the motor.